About your trailer.
Are the crossbars above the frame?
Most of us have moved the crossbars under the frame which lowers the boat by 6-9 inches and makes it easier to load.
The trade off is that it gives less space to put a sailbox or tube.
About wheels.
All of the brands are expensive.
Different ones work better under certain conditions.
All of them work good.
It sounds like the Seitech - http://www.seitech.com/m/_general/config15.asp - would be perfect for your needs because it functions like a hand pulled trailer and is easier for one person to control.